JAVA.ARITH.OFLOW : Cast: int Computation to long (Java)

Summary

The result of an integer computation that might overflow is cast into long, with possible loss of precision.

Floating point operations are by nature approximated. This can introduce bugs when precise, mathematical properties are expected from inherently imprecise floating point computations. Moreover, computations that might lose precision or overflow, whose result is stored in a larger type, are suspicious since, by computing on the larger type from the beginning, one could avoid approximations and overflows.

Properties

WARNING_FILTER += discard class="Cast: int Computation to long (Java)"

Example

public class MillisecondsInDays {
  public static void main(String[] args) {
    int days = Integer.parseInt(args[0]);
    long milliseconds = days * 24 * 60 * 60 * 1000; // "Cast: int Computation to long (Java)" warning issued here

    System.out.printf("Inside %d days there are %d milliseconds", days, milliseconds);
  }
}

The computation days * 24 * 60 * 60 * 1000 is performed on integers and then stored into a long. As a consequence, the extra space allowed by a long value is not exploited and the computation will overflow if days is larger than 24.

To avoid this problem, perform the computation with long values, so that the entire long space is available. Overflow will only occur for very large values of days.

public class MillisecondsInDays {
  public static void main(String[] args) {
    int days = Integer.parseInt(args[0]);
    long milliseconds = days * 24L * 60 * 60 * 1000;

    System.out.printf("Inside %d days there are %d milliseconds", days, milliseconds);
  }
}

Resolution

If a large type for the result of a computation is desired, compute from the beginning on that type instead of applying a type conversion at the end of the computation.

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.

• REPORT_SIMILAR_WARNINGS
• WARNING_FILTER